1. Field of the Invention
This invention relates to an internal support structure for an innerspring mattress or similar product. Innerspring mattresses comprise a plurality of coil springs placed in a plurality of rows and columns to form a generally rectangular unit. A top border wire extends around the periphery of the rectangular coil spring unit in the top plane formed by the springs and a bottom border wire similarly extends around the periphery in the bottom plane formed by the springs. The border rows and columns of coil springs are connected to the border wires. All of the coil springs are interconnected with one another. To provide additional reinforcement an internal support unit is located in at least the top plane and is secured to at least some of the coil springs. A second internal support unit is usually symmetrically located in the bottom plane. Once the individual coils have been secured together and the support units connected, the top and bottom planes formed by the springs are covered with padding or cushioning layers and the cushioned spring unit is enclosed within a fabric cover to provide a finished innerspring mattress.
An innerspring mattress unit should provide uniform weight distribution and support for the individual reclining on the mattress. While the degree of firmness is a matter of choice, an innerspring mattress unit should be resilient in the vertical direction and exhibit a minimum distortion in the horizontal direction.
2. Prior Art
Innerspring mattress units in use today frequently have an internal support structure which is positioned at different locations within the mattress. One type of edge supporting device is shown in U.S. Pat. No. 3,327,331, issued to M. Simon on June 27, 1967, entitled "Spring Unit Construction". The reinforcing structure disclosed in this patent is directed primarily to the edge and corner areas of the mattress. There is no supplemental or additional support for the central portion of the mattresses. This type of structure tends to overcompensate at the edge and corner areas resulting in a perceptible imbalance in resilience for the overall mattress.
Another well-known supplementary support structure is disclosed in U.S. Pat. No. 3,242,505, issued to S. Tyhanic on Mar. 29, 1966, entitled "Spring Unit". The central support structure disclosed in the Tyhanic patent includes an inner border wire concentric and coplanar with the standard peripheral border wire. The inner border wire is not directly connected to the outer border wire but is rather free floating. The transverse portions of the inner border wire are connected by several longitudinal bands which are connected by rings or the like to the coil spring which they overlay. While providing some edge and corner support due to the proximity of the inner border wire to the edge of the mattress unit, the Tyhanic patent is primarily directed to a central or middle mattress support structure.
Numerous practical problems occur in the use of these and other known mattress support units. One problem particularly prevalent in the structure disclosed in U.S. Pat. No. 3,242,505 involves the surface layer of padding or foam. The top and bottom surfaces of the coil springs in the mattress tend to move longitudinally relative to the support structure. This movement of the surface loops of the coil springs relative to the support structure causes abrading of the padding or foam layer overlaying the central support structure. The constant abrasion causes the padding layer to force itself between the individual coil springs thereby causing holes in the padding layer in the plane of the top or bottom of the mattress. These holes or gaps in the padding layer make the mattress surface irregular and both uncomfortable and unsightly to the user.
Another problem experienced in mattress support units is the lack of uniform resilience at both the center and the corner areas of the mattress. This problem is accentuated by the user sitting at the corner of the mattress thereby placing an unusual localized force over a small area. Another cause of stress for the corner portions of the mattress is the use of fitted sheets. In order to dress the mattress with a fitted sheet the corner of the mattress must be bowed out of its normal planar position. This abnormal bowing of the corner portion of the mattress results in weakening of the mattress corner or permanent distortion of this area. To correct the problem of non-uniform resilience due to the unusual wear at the corner areas of the mattress localized edge and corner supplementary support units such as described in U.S. Pat. No. 3,327,331 were developed. However, these localized support units result in overcompensation for the corner areas of the mattress. Over a period of time the central mattress area softens or loses resilience while the independently reinforced corner and side areas even with the unusual wear do not correspondingly lose a proportional degree of resilience. This disproportionate wearing results in a "tub" effect wherein the corners and sides are rigid in comparison to the central portion of the mattress.